A module containing a membrane comprising a hydrophobic polysulfonic resin polymer is extensively used in various fields on account of its excellent mechanical characteristics and heat resistance.
However, because of the strong water repellency which is a feature of said material membrane, it is required, in certain cases, to wet the membrane at the time of use in order to develop the performance of the dry membrane for, for example, oxyethylene gas sterilization. For this purpose, it is known to impregnate the membrane with a hydrophilic substance such as glycerine or a surface active agent. Also, various methods were examined for making the membrane itself hydrophilic, and proposals made for improvement of the resistance to contamination and of the adaptability to the living body.
As one of such methods, an attempt was made to make the polymer itself hydrophilic by chemical modification, using sulfonation by concentrated sulfuric acid (Japanese Publication No. SHO 55-36296). However, although this method may make the polymer hydrophilic, the actual performance and quality of the separating membrane are not disclosed, and the membrane forming method is not clearly presented.
For a blend of a polysulfone and a hydrophilic polymer, spinning with addition of a polyvinylpyrrolidone or poly(ethylene glycol) has been examined in order to improve the spinnability (Journal of Applied Polymer Science, Vol. 20, 2377-2394). Also, although the membrane is in the form of a sheet, a method of extracting and removing the hydrophilic polymer after making the membrane by a similar procedure has been shown (Japanese Patent Publication No. SHO 55-106243). Further, Japanese Patent Publication No. SHO 58-104940 indicates a method of cross-linking and fixing the hydrophilic polymer in the membrane by a cross-linking agent or a physicochemical catalyst, but the procedure is very complicated, the intended membrane performance may be damaged, and the effect is hardly said to be satisfactory. Japanese Patent Publication No. SHO 61-93801 shows medial application with the amount of addition of the hydrophilic polymer reduced, but, as noted, complete extraction and removal are difficult.
Also, in Japanese Patent Publications Nos. SHO 61-238306, SHO 63-97205 and SHO 63-97634, a method of cross-linking and fixing the hydrophilic polymer by heat or radiation treatment are described, but a membrane of small holes substantially preventing albumin from leaking is not provided.
On the other hand, a method of fixing a hydrophilic polymer or compound on the surface of the membrane is disclosed in Japanese Patent publications Nos. SHO 62-11503, SHO 63-68646 and SHO 62-125802. However, the methods shown in these Patent Publications are not always satisfactory in making the membrane hydrophilic or unable to suppress elution of the hydrophilic compound from the membrane at the time of actual use, and are not practically applicable to the medical or industrial field where a high degree of cleanliness is required.